Most people don't consider swords as a viable weapon in the future. However they are still used in many ceremonious capacities, and most likely will still be used in that way for many years to come. But there are circumstances in which the sword could return in one form or another to use as a weapon. Many science fiction authors have toyed with the idea. They have found four possibilities, that I have found, for the sword's return.

One: a worldwide catastrophe that leaves nations without a industrial base. Under such conditions the production of firearms and ammunition would by limited until the factories could be rebuilt. During which time the sword could be used instead. Or the technology to make firearms could be lost altogether and swords could return as a mainstream weapon.

Two: a technological development could make firearms obsolete. Such as a discovery in armor or shielding technology that would make projectile weapons useless. Then a second discovery would make it so swords could pierce this armor but firearms could not. An example would a force-shield that could deflect or disintegrate small bullets but could not stop a sword made from a new kind of metal.

Three: the classic "light saber" idea. A technique is found that allows the user of the sword to deflect or absorb projectile weapons fire and gives him greater firepower.

Four: some kind of composite sword/projectile weapon is developed that combines the lethal ability of the sword in close quarters and the range of a firearm.

Swords could be in use today if guns were not so widely available and swords so hard to use. A skilled swordsmen using a sword of modern day materials and modern day techniques could possibly defeat two or three gunmen, if they were in relatively close quarters. However this all assumes the swordsmen is well trained and in top physical condition. The gunmen don't need a great deal of training, especially if they have automatic weapons, and they can just sit in one place and shoot at the swordsmen. So today the gun reigns as the weapon of choice, but who knows about tomorrow.